Transmission control

ABSTRACT

An automatic transmission control having an overdrive shift valve whose operation is controlled by an overdrive governor pressure control valve which in turn is controlled by an overdrive solenoid valve that is under vehicle operator control, there being further included an overdrive accumulator that operates to establish fluid delivery for establishment of all of the transmission&#39;&#39;s lower speed drives and also operates as both a valve and an accumulator to effect establishment of and cushion overdrive engagement.

0 United States Patent 1 [111 3,724,292

Borman 51 Apr. 3, 1973 54] TRANSMISSION CONTROL 3,497,043 2/1970 Leonard..74/869 x Inventor: August H. Borman, Farmington, 3,625,090 12/1971Chana ..74/869 X Mlch' Primary Examiner-Charles J. Myhre [73] Assignee:General Motors Corporation, Assistant ExaminerThomas C. Perry Detroit,Mich. Attorney-'W. E. Finken, A. M. Heiter and R. L. Phil- 22 Filed:Mar. 12,1971- 21 Appl. No.: 123,625 57 ABSTRACT An automatictransmission control having an over- [52] U-S- Cl- 5 4/869 drive shiftvalve whose operation is controlled by an [51] Int. Cl. ..B60k 21/02overdrive governor pressure control valve which in [58] Fieldof'seal'ch...............................74/864-869 tum is ontrolled byan overdrive solenoid valve that v is under vehicle operator control,there being further [56] Refere clled included an overdrive accumulatorthat operates to establish fluid delivery for establishment of all ofthe UNITED-STATES PATENTS. transmissions lower speed drives and alsooperates as 2,908,181 10/1959 Smirl ..74/869 X both a valve and anaccumulator to effect establish- 2,926,543 3/1960 Holdeman etal...74/869 ment of and cushion overdrive engagement. 3,001,415 9/1961Smirl... ....74/864 X 3,236,117 2/1966 Christenson ..74/869 3 Claims, 5Drawing Figures PATENTEU 3 I975 SHEET 1 OF 4 [M 1: ATTORNEY PATENTEUAPR3ma 3. 724,292

sum 2 0r 4 lVE NOID VALVE OVERDRIVE PRESSURE CONTROL VALVE 34 SHIFTVALVE 532 ATTORNEY PATENTEUAPRB I975 3,724,292

SHEET 3 OF 4 VACUUM MODULATOR VALVE QDETENT CONTROL VALVE INVENTOR.

flugwzH [imnan m? Z9 XW SERVO ATTORNEY Z1 DEl'ENT SOLENOID VALVEPATENTEDAPR3 I973 I 3, 724,292

saw u UF 4 2 ACCU LATOR VAL LOW AND REVERSE BRAKE SERVO I N VEN'TOR.

ATTORNEY TRANSMISSION CONTROL This invention relates to transmissioncontrols and more particularly to transmission controls for providingshifting to and from overdrive.

The transmission control accordingto the present invention offers asimple system for controlling shiftingto and from overdrive and includesan overdrive shift valve, an overdrive governor pressure control valve,an

overdrive solenoid valve and an overdrive .accuinulav tor. In all of thetransmission drivesbelow .overdrive the overdrive accumulator providesfor delivering fluid pressure to establish direct drive throughoverdrive gearing and then to establish overdrive operates as a valve todiscontinue direct drive by the overdrive gearing while providingpressure control to cushion overdrive engagement. The overdrive shiftvalve is normally spring biased to a downshift position in all drivesbelow overdrive and this spring bias is assisted by a modulator pressurereflective of load torque demand to oppose a governor pressure thatchanges with load speed and acts to urge the overdrive shift valve toits upshift'position to effect establishment of the overdrive. Governorpressure supply to the overdrive shift valve is controlled by anoverdrive governor pressure control valve which is spring biasedto aposition preventing governor pressure delivery and is normally biased byfluid pressure to a governor shut-off position when the transmission isconditioned for automatic shifting. An overdrive solenoid valve underthe control of the vehicle operator controls the establishment ofanother fluid pressure bias on the overdrive governor pressure controlvalve to assist the overdrive governor pressure control valve springbias and urge this valve to its overdrive shift permit position topermit shifting to overdrive.

An object of the present invention is to provide a new and improvedtransmission control for shifting to and from overdrive.

Another object is to provide a transmission control having an overdriveshift valve that operates in response to both load torque demand andload speed to effect shifting to and front overdrive and with shiftingoccurring at a predetermined minimum vehicle speed and with the governorpressure bias being under the manual control of the vehicle operator.

Another object is to provide in a transmission control for shifting toand from overdrive an overdrive shift valve that has an upshift biasthat changes with load speed and a downshift bias provided by a springplus a bias that changes withload torque demand and with theestablishment of the upshift bias controlled by a normally shift preventbiased valve that is in turn controlled to permit shifting by a manuallycontrolled solenoid valve and with there being further included anoverdrive accumulator'tliat operates to deliver fluid pressure to lockout overdrive and also operates to cushion'engagement of overdrive whilepreventing the lock out.

These and other objects will be more apparent from the followingdescription and drawing in which:

A transmission and a control systemthcrefor-according to the presentinvention are shown'in FIGS. 2a, 2b, 2c and 2d when arranged asindicated by FIG. 1.

for

drive, second TRANSMlSSlON DRIVE ARRANGEMENT Referring to FIG. 2a thereis shown a transmission Y a passenger car generally comprising ahydrodynamic torque converter 10, an overdrive and direct drive gearunit 11, and lower ratio drive gear units -12 and 13 all housed in atransmission housing 14. The transmission is operable .to provide fourforward speed range drives, neutral and reverse drive. The four forwardspeed range drives include first gear reduction gear reduction drive,direct drive and overdrive.

Describing now the transmissions structural details, an engine drivenhousing cover 15 and connected impeller cover 16 rotate at engine speedand enclose a fluid chamber 17. Cover 16 drives through a sleeve 18', apump drive gear 19 of a pump 20 which is shown in both FIGS. 2a and 2b,the sleeve 18 being welded to the cover 16 and having a drive lugconnection to the gear 19. Pump 20 is located in a pump housing 21bolted to a transmission support web 22, the web being secured by thesesame bolts to transmission housing 14. Torque converter 10 includes aseries of impeller or pump vanes 24 carried by cover 16, turbine vanes25 carried by a hub '26 and reaction or stator vanes 27 which aresupported on a reaction hub 28 and are disposed between the inner endsof the turbine and impeller vanes. Reaction vanes 27 and hub 28 arepermitted free rotation in the same direction as the impeller andturbinevanes which is the forward direction by a one-way roller typebrake 29 disposed between hub 28 and a ground sleeve 30 that is pressfitted to support web '22. One-way brake 29 prevents reverse rotation ofreaction vanes 27 and hub 28 under the influence of circulating fluid inthe converter. Turbine hub 26 is splined to a turbine shaft 32 whichtransmits the turbine drive to the forwardly located overdrive anddirect drive gear unit 11.

The overdrive and direct drive gear unit 11 is operable toselectivelyprovide an overdrive and direct drive and comprises a simplehelical planetary gear set having a planetcarrier 33 splined to and thusdriven by turbine shaft 32. Carrier .33 supports planet gears or pinions34 in mesh with a ring gear 35 and an annular sun gear 36. A clutch drum37 is drivingly connected to sun gear 36 by having helical splinesengaging extensions of the helical teeth of sun geari36 .as shown. Thisdrum and sun gear connection .is maintained without providing addedaxial stop means by the equal and opposite torques on drum 37 and sungear 36 during operation. The clutch drum 37 is also drivingly'connected by splines to a plurality of friction plates 38 that areadapted to engage friction plates 39. The plates 39 are drivinglyconnected'by splines to planet carrier 33,

the plates 38 and 39 forming a part of a lockout clutch indicatedgenerally as 41. A piston 42 forms with drum 'to drum 37 and are adaptedto engage friction plates 50. The plates 50 are connected by splines toa brake housing 51 which is fixed to transmission housing 14. A piston52 forms with housing 51 a servo chamber 53 that is adapted to'receivefluid under pressure to engage overdrive brake 48. Springs 54 seated atone end upon the stationary brake housing 51 and at the other end on aspring seat 55 carried by piston 52 bias piston 52 towards its releaseposition.

Ring gear 35 is pinned to and thus fixed for rotation with a clutch drum57 of a forward drive clutch indicated generally at 58. Drive frictionplates 59 drivingly connected by splines to drum 57 are adapted toengage driven friction plates 60 which are drivingly connected bysplines to a clutch hub 61 that is splined to an intermediate driveshaft 62. A piston 63 forms with drum 57 a pair of servo chambers 64 and65 that are adapted to receive fluid under pressure to engage forwarddrive clutch 58. Release springs 66 seated upon a spring seat 67 carriedby drum 57 bias piston 63 towards its clutch release position. Fluidpressure for engaging forward drive clutch 58 may be admitted tochambers 64 and 65 by a passage 68 through turbine shaft 32 and clutchdrum 57.

g A direct drive clutch indicated generally at 69 comprises a driveclutch hub 70 splined to drum 57, drive friction plates 71 drivinglyconnected by splines to hub 70 and driven friction plates 72 which aredriving'ly connected by splines to a driven clutch drum 73 and areadapted to engage plates 71. A piston74 forms with drum 73a pair ofservo chambers 75 and 76 which are adapted to receive fluid underpressure to engage direct drive clutch 69. Springs 77 seated upon aspring seat 78 carried on clutch drum 73 bias piston 74 towards itsclutch release position. Clutch drum 73 is splined to the forward end of'a sleeve shaft 79 and is rotatably supported upon an axially extendingsupport boss 80 of a support web 81 which is fixed by splines totransmission housing 14. Fluid pressure may beadmitted to chamber 75through a passage 82 in boss 80 and 'a passage 83 in drum 73 to engagedirect drive clutch 69. Fluid pressure may also be admitted to chamber76 through a passage 84 in boss 80 and a passage 85 in drum 73 to engagedirect drive clutch 69. An overrun band brake 86 grounded to thetransmission housing 14 and operated by a fluid pressure operated servomotor 87 shown in FIG. may, a

times, be applied to hold drum 73.

The stationary support web 81 is shaped on its front side to receive apiston 90 which forms with web 81 a servo chamber 91 that is adapted toreceive fluid under pressure. Friction plates 93 splined to housing 14are adapted to engage friction plates 94 splined to a hub 95, thisstructure providing a second gear brake indicated generally as 96. Fluidpressure may be admitted to chamber 91 through a passage 97 in supportweb 81 to engage brake 96. Springs 98 seated upon .a spring seat 99carried on web 81 bias piston 90 towards its brake release position. v y

A one-way sprag type brake 100 isdisposed between hub 95 and a race 101that is press fitted to clutch drum 73. The one-way brake 100 operateswhen brake 96 is engaged to permit free forward rotation of clutch drum73 and prevents reverse rotation.

The rear gear unit 13 comprises a simple helical planetary gear sethaving an annular sun gear 102, a ring gear 103 and a planet carrier 104having planet pinions 105 in mesh with sun gear 102 and ring gear 103.The sun gear 102 is splined to the rear end of sleeve shaft 79, the ringgear 103 is formed on a drum 106 which is splined at its hub 107 to therear end of intermediate drive shaft 62, and the carrier 104 is splinedto a flange 108 that is integral with a shaft 109. The shaft 109 issupported for rotation by the transmission housing 14 as shown andserves as the transmissions output. v

The gear unit 12 located forward of gear unit 13 comprises a simplehelical planetary gear set having an annular sun gear 110 formedintegral with sun gear 102, a ring gear 111 formed integral with carrier104 and a planet carrier 112 having planet pinions 113 in mesh with sungear 110 and ring gear 111. Carrier 112 is supported for rotation on aboss 114 projectingfrom the rear side of web 81. A low and reverse handbrake 11S grounded to the transmission housing 14 and operated by afluid pressure operated servo motor 116 shown in FIG. 2d is adapted toengage a brake drum 117 formed on carrier 112. In addition to thisselective holding of carrier 112, there is provided a one-way rollertype brake 118 having a cam ring pinned to carrier 112 and an inner racepinned to the stationary web 81 The one way brake 1 18 operates toprevent reverse rotation of carrier 1 12 and permits free forwardrotation.

OPERATION OF THE TRANSMISSION DRIVE ARRANGEMENT The transmission drivearrangement affords at least four forward speed range drives, neutraland a reverse speed range drive. These drives may also be called thetransmission's gear ratios. The forward drives make available threeforward drive ranges which will be referred to as drive range,intermediate range and low range.

For neutral, clutch 41 is engaged but all other friction driveestablishing devices are released so that no power from turbine shaft 32can be transmitted through the gearing to output shaft 109.

In drive range three forward drive ratios may be obtained withautomatically operable controls including first or lowest gear drive,second gear drive and direct drive. In addition a fourth gear drive,overdrive, may be had by manual selection at vehicle speeds above apredetermined speed.

v Drive range first or low gear drive is obtained by engaging lockoutclutch 41 and forward drive clutch 58. Power from the forwardly rotatingturbine shaft 32 is delivered through carrier 33 and ring gear 35 toclutch drum 57 with the overdrive and direct drive gear unit 11 lockedup by the engaged lockout clutch '41 and thus providing a l:l speedratio drive between carrier 33 and drum 57. Power flows through theengaged forward drive clutch 58 and intermediate, drive shaft 62 todrive ring gear 103 in gear unit 13forwardly. Assuming a load on outputshaft 109 and thus on planet carrier 104, this carrier tends to remainstationary so that sun gears 102 and 110 in gear units 12 and 13 aredriven in reverse. In gear unit 12, power input to planet pinions 113from sun gear 110 tends to cause planet carrier 1 12 to rotatebackwardly but such rotation is prevented by one-waybrake 118. Planetpinions 113 therefore drive ring gear .111 and thus output 7 shaft 109forwardly. In low gear, drive is at the compound reduction ratio thusprovided by the interconnected gear units 12 and 13. Due to the actionof one-way brake 118, the transmission will not transmit power fromoutput to input for engine braking in drive range low gear.

Drive range second gear drive is accomplished by retaining engagement ofclutches 41 and 58 and engaging brake 96. Brake 96 and one-way brake 100in series therewith prevent reverse rotation of clutch drum 73, shaft 79and thus sun gears 110 and 102. Power is applied to ring gear 103 andwith sun gear 102 held against reverse rotation, carrier 104 and thusoutput shaft 109 are driven forwardly at the reduction ratio of gearunit 13. One-way brake 100 permits free forward rotation of sun gear 102and thus power cannot be transmitted from output to input for enginebraking.

Drive range direct drive is accomplished by maintaining clutches 41 and58 engaged and engaging direct drive clutch 69. One-way brake 100permits forward rotation of drum 73 and thus forward driveof sun gears110 and 102 irrespective of the retained engagement of brake 96. Sinceboth ring gear 103 and sun gear 102 in gear unit 13 are driven at thesame speed, the gear unit 13 is locked up to provide a 1:1 speed ratioor direct drive to drive output shaft 109.

Drive range overdrive is accomplished by maintaining clutches 58 and 69and brake 96 engaged and by releasing lockout clutch 41 and engagingoverdrive brake 48. With brake 48 engaged and clutch 41 released, sungear 36 is held against rotation in either direction and ring gear 35and connected clutch drum 57 are driven at a speed faster than shaft 32by the overdrive ratio thus provided by gear unit 11. Since gear unit 13is maintained in its directd'rive condition by clutches 58 and 69, anoverdrive gear ratio is provided to drive output shaft 109 faster thanturbine shaft 32.

In intermediate range operation only the first and second gear ratiosare made available since this range is intended for rapid vehicleacceleration ormaximum performance and also second gear braking. Forintermediate range first gear drive the clutches 41' and 58 are engagedin the same manner as when operating in drive range.

Intermediate range second gear operation is obtained by engagingclutches 41 and 58 in the same manner as when operating in drive rangesecond gear drive except with the additional engagement of brake 96. Thetransmission controls in intermediate range will, however, prevent anupshift from second gear drive to direct drive regardless of vehiclespeed.

Low range operation is provided primarily for overrun or downhill enginebraking. First and second gear drives may be had in low range operation.Low range first gear drive is obtained by engaging clutches 41 and 58and brake 115. Blake 1 15 prevents rotation of carrier 1 12duringoverrun to provide engine braking. In low range operation thetransmission controls prevent an upshift from first to second gear driveuntil the vehicle speed substantially exceeds the speed at which a firstto second gear drive upshift occurs'when operating in drive orintermediate range. Low range second gear drive is accomplished byengaging clutches 41 and 58 and brake 86 and releasing brake 115.

Reverse drive is obtained by engaging clutches 41 and 69 and brake 115.The gear unit 11 is thus locked up and provides al:l speed ratio driveto ring gear 35 from which drive is through clutch drum 57, clutch 69and shaft 79 to sun gears and 102. Since forward drive clutch 58 isreleased, gear unit 13 has no reaction point and ring gear 103 rotatesfree. Carrier 112 is held by brake 115 and planet pinions 113 drive ringgear 1 11 and connected output shaft 109 in reverse.

TRANSMISSION CONTROL SYSTEM The present invention is embodied in thetransmission control system shown in FIGS. 2a, 2b, 2c and 2d which isadapted to control transmission drive arrangements of the type shown inFIG. 2a and described above. Generally, the transmission control systemis operable to establish the transmission in neutral and park conditionsand to provide three selective forward drive range conditions providingdifferent modes of operation and also to provide a reverse drivecondition.

Pump

The fluid such as oil used in the control system is returned to a'sumpshown in FIG. 2b via-various exhausts in the systems components, thesump being secured to the underside of the transmission housing 14.Fluid pressure for the control system is supplied by the positivedisplacement pump 20' which is input driven as described above and isconnected as shown in FIG. 2b to draw fluid from sump 120 throughasuction passage 121 having a filter 122 therein. Fluid is deliveredfrom pump 20 to a main passage 124 that is always connected to deliverfluid to a main pressure regulator valve 126 shown in FIG. 2b, a manualvalve Main Pressure Regulator Valve The main pressure regulatorvalve 126regulates the pressure in main passage 124 and comprises a spool valveelement 138 having spaced lands a, b and c of equal diameter located inbore 139 of the pumps body. Fluid from pump 20 is delivered via mainpassage 124 to valve element 138 always between lands a and b and thenthrough a flow restrictive passage 140 to a chamber 141 which is formedby plugging the upper end of bore 139.

The lower end of valve element 138 contacts a spool member'l42 having aland a and a larger land b located in-an accommodating stepped borel43'in' a sleeved portion of the pump body. The lower end of bore 143 isclosed to provide a chamber 144 to receive a pressure which normallyvaries as a function of engine intake manifold pressure and vehiclespeed as described in more detail later. The space between lands a and bof spool member 142 is connected to receive the pressure providing forestablishment of the transmissions reverse drive as described in moredetail later with such pressure acting on the unbalanced area of land bto urge'the regulator valve-element 138 upward.

The valve element .138 is normally biased to the position shown by aspring 145 and with pump pressure supplied to chamber 141', valveelement 138 is urged downward by this pressure against the bias ofspring 145 to regulate the pressure in main passage 124 at a valuedetermined by the spring bias with the overage being exhausted firstbetween lands a and b to a converter feed passage 146 and then betweenlands b and c to the pump intake passage 121 on continued downward valveelement movement. The converter feed passage 146 is'connected to deliverfluid to the torque converter 10 as shown in FIG. 2a with fluid from theconverter being returned via a passage 148 to a transmission lubricationpassage 149 through an oil cooler 150. An oil cooler bypass valve 152 isoperable to at times bypass oil cooler 150, particularly when the oil iscold, by connecting converter return passage 148 to lubrication passage149 ahead of cooler 150.

The above described main pressure regulation assumes that only springbias is determining pressure. Considering now that, pressure indicativeof engine torque demand and vehicle speed acts in chamber 144 on land aof spool member 142, this member is urged upward and assists the spring145 in controlling main pressure so that main pressure then increaseswith increase in this controlling pressure. In reverse, main pressurewhich is used to establish the reverse drive is supplied to spool member142 between lands a and b where it acts on the unbalanced area of land 5to assist passage 162 remains blockedfrom the main passage 124 by land0. When valve element 158 is moved to the spring 145 and thus boost mainpressure to a high value.

Manual Valve The manual valve 128 determines the operation of thecontrol system and thus that of the transmission drive arrangement andcomprises a spool valve element 158 having spaced lands a, b, c, d and eof equal diameter located in bore 159 of the valve body. The valveelement 158 is movable to six positions which are park (P), reverse (R),neutral (N), drive range (D), intermediate range (INT) and low range(L). The valve element 158 is adapted at its left end to be operatedthrough suitable conventional linkage including a pin 160 by theoperator of the vehicle who manually selects the valves position.

When the valve element 158 is in the D position as N position, the mainpassage 124 is connected between lands c and d to thereverse-neutral-drive passage 162 and is blocked from all other passagesleading from this valve. When valve element 158 is moved to the Rposition, the main passage 124 remains connected to thereverse-neutral-drive passage 162 and is in addition connected betweenlands 0 and 'd to a reverse drive passage 168 which is connected bypassages 84 and 85 to chamber '76 of the servo that operates directdrive clutch 69. When valve element 158 is moved to the P position, themain passage 124 is blocked by land e so that main pressure is preventedfrom reaching any of the passages in the valve.

Two exhausts 169 and 170 are provided for the bore 159 as shown so thatin the P position, the exhaust 169 is connected to only the reversedrive passage 168 and the reverse-neutral-drive passage 162'while theother exhaust 170 is connected to only the low range passage 166,intermediate range passage 164 and drive range passage 161. In the Rposition, the exhaust 169 is blocked by land c while'exhaust 170 isconnected to only the low range passage 166, intermediate range passage164 and drive range passage 16] In the N position, the exhaust 169 isconnected to the reverse drive passage 168 while exhaust 170 isconnected to only the low range passage 166, intermediate range passage164 and drive range passage 161. In the D position, the exhaust 169 isconnected to only the reverse drive passage 168 while the exhaust 170 isconnected to only the low range passage 166 and the intermediate rangepassage 164. In the [NT position, the exhaust 169 is .connected toonlythe reverse drive passage 168 and the reverse-neutral-drive passage 162while the other shown, main passage 124 is connected between lands c andd to a drive range passage 161 and also to a reverse-n'eutral-drivepassage 162. The drive range passage 161 is connected via passage 68 tochambers 64 and 65 of the servo that operates the forward drive clutch58 with the connection to chamber 64 being through a flow restriction163. When valve element 158 is moved to the INT position, main passage124 remains connected to drive range passage 161 and is in additionconnected between lands d and e to an intermediate range passage 164while land 0 blocks the main: passage 124 from thereverse-neutral-dri've passage 162, this latter passage being allowed toexhaust through port 169. When valve element 158 is moved to the Lposition, the main passage 124 remains connected to both the drive rangepassage 161 and the intermediate' range passage 164, the latterconnection I now being providedbetween lands 0 and d, and the mainpassage 124 is in addition connected between exhaust 170 is connected toonly the low range passage 166. In the L position, the exhaust 169 isconnected to only the reverse drive passage 168 and thereverseneutral-drive passage 162 while the other exhaust 170 is blockedfrom all the fluid passages by land e.

Governor Valve Vacuum Modulator Valve ,The vacuum modulator valvetranslates load and torque demand from engine manifold vacuum,barometric pressure or altitude and speed or governor pressure intomodulator pressure in a modulator passage 178. V I

' The modulator valve 130 has a regulator spool valve element 179'having spaced lands a, b and c of equal diameter located in a bore 181of the valve body and a land d of larger diameter located in an enlargedbore portion 182. The left end of bore 181 is closed to provide achamber 184 which is connected through a flow restriction 186 to themodulator passage 178. The bore 182 to the right of land d is vented byan exhaust 188.

A conventional altitude compensating vacuum modulator 189 has a housing191 which is fixed to the vacuum modulator valve body. A diaphragm 192divides the housing into a vacuum chamber 194 and an atmospheric chamber196, the vacuum chamber 194 being connected to the engines intakemanifold via an engine manifold vacuum passage 197 and the atmosphericchamber 196 being opened to atmosphere. A rigid U-shaped strut assembly198 connects the diaphragm 192 to a sleeve member 199 which is arrangedto engage the right-hand end 200 of the modulator valve element 179. Ananeroid or evacuated closed bellows 201 is fixed at one end to thehousing 191 and at the other end is fixed to the diaphragm 192 and strutassembly 198. The atmospheric pressure acting to collapse the bellowsagainst the resilience thereof or a spring therein and a modifying orcalibrating spring 202 provides a force acting through the strut to biasthe valve element 179 to the left for increased modulator pressure inmodulator passage 178. Increasing engine vacuum in chamber 194 anddecreasing atmospheric pressure acting on bellows 201 reduces this forceand thus the modulated pressure.

The vacuum modulator 189 applies through sleeve 199 a force to valveelement 179 to tend to connect the main passage 124 between lands b andc to modulator passage 178 to increase modulator pressure whilemodulator pressure via flow' restriction 186 acts in chamber 184 to biasthe valve to tend to connect the modulator passage 178 between lands aand b to a normally exhausted detent passage 204 while land b blocks themodulator passage 178 from the main passage 124. Thus, the modulatorpressure in modulator passage 17 8 increases with decreasing vacuum orincreasing load torque demand but is decreased with increased altitude.The governor passage 176 is connected through a flow restriction 206 todeliver governor pressure to the space between lands c and d so it actson the unbalanced area of land d to reduce modulator pressure withincreasing transmission output speed and thus vehicle speed. In afull-throttle through-detent condition, the modulator force issufficiently high enough to cause the valve element 179 to moverightward to connect the detent passage 204 to the modulator passage178, the detent pressure in passage 204 which is equivalent to a fixedpressure as described in more detail later is delivered to modulatorpassage 178 so that the modulator pressure is either modulated or is atthis fixed pressure, whichever is higher. A ball valve 209 shown in FIG.2b is normally biased by modulator pressure to effect modulator pressuredelivery to the main pressure regulator valve 126. Valve 209 is biasedby the pressure of fluid supplied to intermediate range passage 164 toconnect the intermediate range passage 164 via the modulator passage 178to the main pressure regulator valve 126 to boost main pressure forintermediate and also low range. operation while blocking intermediaterange pressure from all other modulator pressure delivery.

Detent Control Valve and Detent Solenoid Valve The detent control valve132 and detent solenoid valve 134 control the pressure in the detentpassage 204 to provide for detent or full throttle downshifts. Thedetent control valve 132 comprises a spool valve element 210 havingspaced lands a' and b of equal diameter located in a bore 211 of thevalve body and a regulator valve element 214 having spaced lands a, b, cand d of equal diameter which are smaller in diameter 1 than the landsof valve element 210 and are located in a smaller diameter bore portion216 of the valve body. The right end of bore 211 is closed by a plug 217to provide a chamber 218 which is connected to the main passage 124through a flow restriction 219. The detent solenoid valve 134 is alsoconnected to the main passage 124 through 'the flow restriction 219 andis in direct communication with chamber 218 of the detent control valve132. The detent solenoid valve 134 has a valve member 220 which isnormally spring biased to close an exhaust port 221 to thereby permitpressure to build in chamber 218 of the detent control valve to fullmain pressure. The detent solenoid valve 134 is operated by anaccelerator pedal 224 that controls the engine throttle. When theaccelerator pedal is moved to a detent position whichoccurs only afterthe engine carburetor throttle valve has been first fully opened toprovide full engine power, it effects closure of a switch 225 to connectthe vehicles battery 226 via conductor line 228 to energize thedetentsolenoid valve 134 so that the valve element 220 is moved to openthe exhaust port 221 to thus prevent pressure from building in chamber218 of the detent control valve 132 by reason of the exhaust port 221being larger than flow restriction 219. Thus, before the engine throttlereaches the detent position, the detent solenoid valve 134 remainsclosed so that pressure builds in chamber 218 of the detent controlvalve to hold the detent valve train against the bias of a spring 229 inthe position shown which will be called the normal position. In thenormal position the modulator passage 178 is .connected between lands aand b of the detent valve element 210 to a shift modulator l passage 230while the detent line 204 is connected between lands a and b of theregulator valve element 214 to the low range passage which it will berecalled is exhausted except in low range operation. On exhaust ofchamber 218 by detent solenoid valve 134, the spring 229 moves thedetent valve element 210 rightward against the plug 217 to a detentposition in which the modulator passage 178 is disconnected from theshift modulator I passage 230. The drive range passage 161 is alwaysopen to the valve element 214 between lands b and c and this space is inturn connected through a flow restriction provided by a groove 231 outin land 0 to the space between lands 0 and d of this valve element. Thespace between lands cand d is in turn connected via a chamber 232 to thedetent passage 204. The pressure in chamber 232 9 chamber 232 is alsoconnected to the shift modulator I passage 230 and thus the regulateddetent pressure is establishedin both the detent passage 204 and theshift modulator 1 pressure passage 230. The left end of bore 216 isclosed to provide a chamber 234 which is connected to the low rangepassage 166. Thus the'valve' Overdrive Governor Pressure Control ValveAnd Overdrive Solenoid Valve The overdrive governor pressure controlvalve 136 and an overdrive solenoid valve 236 provide manual control forthe selection of the fourth forward drive which is overdrive. Theoverdrive governor pressure control valve 136 comprises a spool valveelement 238 having spaced lands a and b of equal diameter located in abore 239 of the valve body. Both ends of the bore 239 are closed toprovide a chamber 241 which is connected to the reverse-neutral-drivepassage 1'62 and a chamber 242 which is connected through a flowrestriction 244 to the main passage 124. Chamber 242 is also connectedto the overdrive solenoid valve 236 which has a valve element 246 thatis normally spring biased to close an'exhaust port 248 as shown topermit the pressure in chamber 242 to build to full main pressure. Theoverdrive solenoid valve 236 is energized by the vehicle operatorclosing a switch 249 so that power is transmitted to this drive by aconductor line 250 from the vehicles storage battery 226. When theoverdrive solenoid valve 236 is energized, the exhaust port 248 is 254which is then connected between lands a and b to a an exhaust port 256.Alternatively,vwhen the overdrive switch 249 is closed to energize theoverdrivesolenoid valve 236 to exhaust the chamber 242, and when themanual valve 128 is positioned in either reverse, neutral or driverange, the main pressure then present in the reverse-neutral-drivepassage 162 and thus in the chamber 241 acts on the left end of land ato move the valve element 238 to a governor pressure delivery positionas shown in which the governor passage 176 is connected between lands aand b to the 34 governor passage 254 while the exhaust port 256 isblocked by land a. When the overdrive solenoid valve 236 remainsdeenergized and thus closed by the overdrive switch 249 remaining openso that full main pressure is in the chamber 242, subsequent delivery offull main pressure to chamber 241 is noteffective to move this valve tocondition the overdrive pressure control valve 136 in itsgovernorpressure delivery position sincethe oppositely acting pressures arebalanced with the result that the spring 252 alone maintains the cutoffposition.

1-2 Shift Valve A l-2 shift valve 258- shown in FIG. 2a controlsshifting between the first and second forward drives and comprises threespool valve elements; namely, a shift valve element 259, a detent valveelement 260, and a regulator valve element 261. The shift valve element259 has spaced lands a, b and c located in a bore 262 of the valve body,land 0 being larger in diameter than the other lands. The right end ofbore 262 is closed to provide a chamber 264 which is connected to thegovernor passage 176 so that governor pressure acts on the right end ofland a to tend to move shift valve element 259 in the leftward directionto an upshift position which is against the downshift biasing forcetransmitted by the l-2 detent valve element 260.

in the first forward drive or downshift position as shown, the shiftvalve element 259 connects a 2-3 drive passage 266 between its lands aand b to an exhaust port 267 while the drive range passage 161 isblocked by land b from the 2-3 drive passage 266. When the shift valveelement 259 is moved leftward by governor pressure to an upshift orsecond forward drive position, land a then blocks the exhaust port 267while the drive range passage 161 is then connected between lands a andb to the 2-3 drive passage 266. Land b has a slightly larger diameterthan land a and bore 262 is stepped accordingly torprovide a hysteresiseffect to hold shift valve' element 259 in the upshift position toprevent valve hunting. The low range passage 166 is always connected toa chamber 269 between lands b and c of shift valve element 259. Achamber 270 between valve elements 259 and 260 is always connected to anexhaust port 272.

The detent valve element 260 and the regulator valve element 261 and aspring 274 arranged between and engaging these elements determine adownshift biasing force that is transmitted by the detent valve elementto oppose the governor pressure force on the shift valve element 259.The detent-valve element 260. has spaced lands a and b located in a bore276, these lands being smallerin diameter than those of the shift valveelement 259. The regulator valve element 261 has spaced, lands a and blocated in a bore 278 with the diameter of these lands being smallerthan the land diameter of the detent valve element 260. In the l-2 shiftvalve downshift position, a shift modulator ll passage 280 is connectedbetween lands a and b of detent valve element 260 to a passage 281 thathas one branch blocked by land a of the detent control valve element 260and another branch which is connected to a chamber 282 at the left endof the regulater valve element 261. The shift modulator ll passage 280is connectible to the shift modulator I passage 230 to receive modulatorpressure as described in more detail later. The modulator pressure inchamber 282 acts on land b of valve element 261 to urge this valveelement rightward against the bias of spring 274 to connect the chamber282 past land b to a passage 284 that is connected to chamber 286between the regulator valve element 261 and the detent valve element260'to thus providein chaniber 286 a pressure which is less than andproportional to modulator pressure. The pressure in'charnber 286 actingon land b of detent valve element 261 and the bias of spring274,.provide a force resisting upshift movement of the l -2- shift valveelement 259. When the governor pressure acting in chamber 264 issufficient to move'the 1-2 shift valve train leftward to the upshiftposition, the shift modulator ll passage 280 is blocked 2-3 Shift ValveA 2-3 shift valve 290 shown in FIG. 2d controls shifting between thesecond andthird forward drives and comprises a shift valve element 291and a modulator valve element 292. The shift valve element 291 hasspaced lands a and b located in a bore 294 of the valve body. The rightend of bore 294 is closed to provide a chamber 295 which is connectedtothe governorpassage 176 so that governor pressure acts onthe right endof land a to tend to move the valve element 291 leftward from adownshift position to an upshift position.

In the downshift position, the shift valve element 291 connects thereverse drive passage 168 between lands a and b to a direct drive clutchpassage 296 while land b blocks the 2-3 drive passage 266 downstream ofa flow restriction 298. When the shift valve element 291 is moved bygovernor pressure to the upshift position, land a blocks the reversedrive passage 168 while the 2- 3 drive passage 266 is then connectedthrough flow restriction 298 and between lands a and b to the directdrive clutch passage296. Land b has a slightly larger diameter than landa and bore 294 is stepped accordingly to provide a hysteresis effect to'hold shift valve element 291 in the upshift position to prevent valvehunting.

The modulator valve element 292 transmits a downshift biasing force tothe shift valve element 291 opposing the upshift governor bias and haslands a, b, c and d of progressively smaller diameter located in a bore299 which is stepped accordingly. A spring 300 is arranged to bias thevalve elements 291 and 292 apart while a spring 301 having a largerspring forceand seated on a pin 302 acts on the modulator valve element292 to urge the shift va'lve element 291 to its downshift position. Inthe downshift position, the shift modulator II passage 280 is connectedpast-land c to a chamber 304 where it acts on the unbalanced area ofland b to thus provide a modulator pressure bias in addition to the biasof spring 301 to hold the shift valve element in its downshift position.When the valve train is moved by governor pressure to the upshiftposition, chamber 304 is blocked by land from the shift modulator IIpassage 280 which is then connected to a chamber 306 where it acts onthe unbalanced area of land 0 to provide a lower modulator pressure biasurging downshifting. The detent passage 204 is always connected to achamber 308 so that when detent pressure is made available to the detentpassage 204, this pressure acts on the unbalanced area of land a to urgethe shift valve element 291 to the downshift position. The intermediaterange passage 164 is connected to a chamber 309 so that whenintermediate range pressure is made available, this pressure acts on theleft end of the shift valve element 291 to hold the shift valve elementin its downshift position. I

3-2 Shift Valve A 3-2 shift valve 311 shown in FIG. 2d controls deliveryof modulator pressure to the 2-3 shift valve 290 to control downshiftingfrom third to second forward drive. The 3-2 shift valve 311 comprises ashift valve element 312 having spaced lands a and b located in a bore314 of the valve body. The left end of bore 314 is closed by a plug 316to provide a chamber 318 in which is located a spring 319 that urgesvalve element 312 to a modulator pressure delivery position as shown inwhich there is provided open connection of the shift modulator I'passage230 via chamber 318 and past the end of land b to the shift modulator IIpassage 280 and thus to-the .2-3 shift valve 290. The rightend of bore314 is closed to provide a chamber 321 to which the direct drive clutchpassage 296 is connected so that when this passage receives fluidpressure to establish the third forward drive as described in moredetaillater, this pressure acting in chamber 321 on the end of land a acts tourge element 312 leftward to a detent pressure delivery position inwhich the detent passage 194 is connected between lands a andbto theshift modulator II passage 280 while this latter-passage is blocked byland b from the shift modulator I passage 230. Thus detent pressure maythen act on the 2-3 shift valve 290 where before modulator pressureacted to provide downshift bias thereon. When detent pressure issupplied to the shift modulator I passage 230, this pressure plus thebias of spring 319 is effective to hold the valve element 312 in themodulator pressure delivery position shown against any clutch pressureacting in charnber 321 for reasons which will become more apparentlater.

3-4 Shift Valve shift valve element 326 is in the downshift position asshown, the drive range passage 161 downstream of a flow restriction 330is blocked by land b while an overdrive brake passage 331 is connectedbetween lands a and b and then through a flow restriction 332 to anexhaust port 334 and a lockout clutch passage 336 is blocked at bore 328between lands b and c. Overdrive brake passage 331 is connected tochamber 53 of the servo that operates the overdrive brake 48 and lockoutclutch passage 336 is connected via passages 46 and 47 to chamber 43 ofthe servo that operates the lockout clutch 41.. The right end of bore328 is closed to provide a chamber 338 which is connected to the 3-4governor passage 254. When the governor pressure delivered to chamber338 to act on the right end of land a is sufficient to inove shift valveelement 326 leftward to an upshift position-against the downshiftbiasing force as described in more detail later, the drive range passage161 is then connected between lands a and b to the overdrive brakepassage 331 while the lockout clutch passage 336 is connectedbetween-lands b andc and then through a flow restriction 339 to anexhaust port 340 and the exhaust port 334 is blocked by land a. Land bhas a slightly larger diameter than land a and bore 328 is steppedaccordingly to provide a hysteresis effect to hold shift valve element326 in the .upshift position to prevent valvehuriting.

The modulator valve element 327 transmits 'a downshift biasing force tothe shift valve element 326 and has lands a'and' b of equal diameter andlands and d of different and smaller diameters located in a bore 342which is stepped accordingly. A spring 344 seated 'on pin 346 urges themodulator valve element 327 downshift bias resisting the governorupshift bias on the shift valve element 326. When the shift valveelement 326 is in its upshift position, the modulator passage 178 isblocked from the chamber 348 so that modulator pressure then acts on theunbalanced area of land 0 to urge downshifting. The detent passage 204is blocked at the valve bore 342 between lands a and b when the valvetrain is downshifted so that detent pressure provides no pressure biasin that condition and in the upshifted position, is connected past land12 to the chamber 348 where it then acts on the unbalanced area of landb to urge downshifting of shift valve element 326. An exhaust port 349is connected to exhaust any leakage to the space between shift valveelement 326 and modulator valve element 327.

Overdrive Brake Accumulator The overdrive brake accumulator 135 shown inFIG. 2b provides for cushioning the engagement of lockout clutch 41 andcomprises a housing 351 having a bore 352 in'which is mounted a piston354 which slides on a pin 356 that is secured at its lower end to thehousing. The piston 354 divides the interior of the housing intochambers 358 and 359. A spring 361 biases the piston 354 to the positionshown to block the main passage 124 from the lockout clutch passage336-, the overdrive brake passage 331 being connected to the otherchamber 359. A ball valve 364 in the main passage 124 operates to closea flow restrictive port 368 so that a smaller flow restrictive port 369delivers fluid at a slow rate to the overdrive brake accumulator andopens to permit fast flow through port 368 in the opposite direction.When fluid is supplied through the flow restrictive port 369 to chamber358 at the slow rate,

1 the piston 354 is stroked downward against the bias of spring 361 andeffects connection of the main passage 124 to the lockout clutch passage336 to provide smooth engagement of the lockout clutch 41 under thecontrol of the flow restriction 369 and the bias. of spring 361. Then,when the overdrive brake 48 is engaged by supplyof fluid pressure to theoverdrive brake passage 331, this pressure is delivered to chamber 359where it assists spring 361 in stroking the piston 354 back to theposition shown with the fluid exiting from chamber 358 at a fast flowrate by the ball valve 364 opening to permit flow through the large flowrestriction 368 to rapidly release lockout clutch 41.

Overrun Brake Servo muitiple accumulator action to cushion both a 2-3upshift and a 3-2 downshift. The overrun brake servo 87 comprises ahousing 371 having a bore 372 in which is mounted two pistons 374 and376. The piston 374 is mounted on pin 378 which is slideably mounted inthe housing and is operatively'connected to the hand brake 86 by anysuitable conventional mechanical linkage, not shown. The other piston376is mounted to slide on a pin 379 which is fixed at its lower end to thehousing 371. The piston 374 separates a chamber 381 at the closed upperend of the bore 372 from a chamber 384 intermediate the piston 374 andthe other piston 376.

The piston 376 separates chamber 384 from a chamber 386 provided at theclosed lower end of bore 372-. A spring 388 located in chamber 381 isseated upon a spring seat 389 carried by pin 378 and biases piston 374toward a release position disengaging the band brake 86. Piston 374 isarranged to contact a snap ring 390 on pin 378 to move the pin upwardlytoward an engage position to engage band brake 86. The other piston 376is normally biased to the position shown by a spring 391 located in thelower chamber 386. The reverse-neutral-drive passage 162 is connected tochamber 381, the 2-3 drive passage .266 is connected to chamber 384 andthe direct drive clutch passage 296 is coi'mected to chamber 386. In thereverse-neutral-drive passage 162 leading to chamber 381 there isprovided a ball valve 396 which is operable to close and open a flowrestriction 397. When flow is directed toward chamber 381 of the overrunbrake servo, ball valve 396 closes flow restriction 397 so that thefluid is required to flow through a smaller flow restriction 398 andthus at a slow rate. When flow is in the opposite direction, the ballvalve 396 unseats to open the flow restriction 397 so that the flow inthe opposite direction is at a faster rate. In the 2-3 drive passage 266leading to chamber 384, there is provided a ball valve 400 which isoperable to close and open a flow restriction 401.

Whenflow is directed toward chamber 384 the ball valve 400 closes flowrestriction 401 so that the fluid is required to flow through a smallerflow restriction 402 and thus at a slow rate. When flow is from chamber384 the ball 400 opens the flow restriction 401 so that return flowoccurs at a faster rate. In the direct drive clutch passage 296 leadingto both the chamber of the direct drive clutch 69 and chamber 386 of theoverrun brake servo 87 there is provided a ball valve 407 which isoperable to open and'close a flow restriction 408. When flow is from the2-3 shift valve 290 toward these devices, the ball valve 407 unseats sothatflow is through flow restriction 408 at a fast rate. When flow is inthe opposite direction the ball valve 407 closes flow restriction 408 sothat the return flow is through a smaller flow restriction 409 and thusat a slower rate.

Low and Reverse Brake Servo and 424. A servo piston 426'is reciprocallymounted in bore 424 and isfixed to an actuator stem 428 which isoperatively connected to operate the handbrake by conventionalmechanical linkage, not shown, there being provided a spring 429 thatbiases piston 426 to its hand release position. An accumulator piston431 has one land mounted in bore 422' and a larger diameter 439 betweenthe pistons 426 and 431, and a chamber 441 above the large diameterportions of pistons 431 and 426. The reverse drive passage 168 and thelow drive passage 166 are connected alternatively by a ball valve 448 toa reverse-low passage 449 which is connected'to chamber 438 of the lowand reverse brake servo 116. When pressure is supplied to the reversedrive passage 168, this pressure operates ball valve 448 to preventfluid in the reverse drive passage 168 from reaching the low drivepassage 166 while the reverse drive passage is connected to thereverse-low passage 449. Alternatively, when the low drive passage 166is receiving fluid pressure, this pressure operates on the ball valve448 to prevent the fluid from reaching the reverse drive passage 168while being delivered to the reverse-low passage 449. On fluid pressuredelivery to chamber 438, the piston 426 is moved upward against the biasof springs 429 and 436 to engage the band brake 115. The 2-3 drivepassage 266 is connected to deliver fluid to chamber 439 of the low andreverse brake servo 116 and also to chamber 91 of the-second gear brake96 through a flow restriction .454-which determines a slow flow rate.During such flow, a ball valve 455 closes a larger flow restriction 456.When flow is in the opposite direction, the ball 455 unseats to openflow restriction 456 so that there is faster fluid flow in the oppositedirection. The remaining chamber 441 is connected-to a l-2 accumulatorpassage 458 which is supplied with fluid pressure as will now bedescribed.

l-2 Accumulator Valve vides a variable accumulator pressure to cushion"the engagement of the second gear brake 96 and comprises a regulatorvalve element 461 having spaced lands a, b, .c and d located in a bore462. Lands b and c are of equaldiameter, land a is of larger diameter,and land d is of smaller diameter andthe bore 462 is steppedaccordingly. A plug 464 is held in place by a pin 466 to close the rightend of bore 462 to provide a chamber 467. Avregulator spring 468 biasesthe valve element 461 rightward to connect the drive range passage 161to the l-2 accumulator passage 458 while closing the latter passage fromthe low drive range passage 166. The l-2 accumulator passage 458 isconnected to chamber 467 so that pressure in this passage acts on thefull end area of land a to urge the valve element leftward against thebias of spring 468. The left end of bore 462 is closedto provide achamber 471 which is connected to the modulator passage 178 througha'flow restriction-472 so that modulator pressure provides a variablebias supplementing the bias of the spring 468 to provide the accumulatorpressure in passage 458 with a value that increases with increasingmodulator pressure. The low range passage 166 is always connected todeliver fluid pressure to act on the unbalanced area of land a to holdthe accumulator valve in its extreme righthand position in which thedrive range passage 161 is fully open to the l-2 accumulator passage458. The detent passage 204 is always connected to deliver any fluidpressure therein to act on the unbalanced area of land 0 to provide anadditional rightward pressure bias to increase the accumulator pressure.

CONTROL SYSTEM OPERATION Neutral With the engine running at idle and themanual valve 128 in its N position for neutral operation, fluid frompump 20 is delivered to main passage 124 which directs.

"from the converter via the converter return passage 148 is directedthrough the cooler 150 and then via the lubrication feed passage 149 tothe transmissions lubrication system, the bypass valve 152 operating toopen to bypass fluid around thecooler from the converter return line 148directly to the lubrication feed passage 149 on the occurrence ofsufficient back pressure immediately upstream of the cooler. As mainpressure continues to increase, the main pressure regulator valve 126-opens further to direct the excess fluid via passage 121 to the suctionside of the pump 20. The manual'valve 128 directs main line pressure tothe reverse-neutral-drive passage 162 which in turn directs thispressure to the overrun brake servo 87 and the overdrive governorpressure control valve 136.

The vacuum modulator valve 130 operates on the main pressure to providemodulator pressure in the modulator passage 178 which directs the latterpressure to the main pressure regulator valve 126 to provide modulationof the main pressure in accordance with engine torque demand, vehiclespeed and altitude.

The modulator pressure is also directed to the l-2 accumulator valve460, the detent control valve 132, and the 3-4 shift valve 324. The onlypressure bias on the detent control valve 132 is that of main pressureand thus the detent control valve is moved to its normal position todirect the modulator pressure via the shift modulator l passage 230 tothe 3-2 shift valve 31 1. The 3-2 shift valve 311 directs the modulatorpressure to the shift modulator ll passage 280 which in turn directsthis pressure to both the 2-3 shift valve 290 and the 1-2 with mainpressure thus actingvon the opposite ends of the valve element 238, thespring 252 operates to hold this valve element in its governor pressurecutoff position so'thatgovernorpressure is not made available to chamber338 of the 3-4 shift valve 324, this chamber instead being exhausted.

directed from chamber 358 to the lockout clutchpassage 336 which in turndirects the pressure to chamber 43 to engage the lockout clutch 41.Thus, all of the shift valves are in their downshift position and withthe forward'drive' clutch 58 released, no torque can be transmittedthrough thegearing irrespective of the fact that the overdrive unitlockout clutch 41 is engaged.

Drive Range First Gear Drive A Then when theinanual valve128-is moved tothe D position to provide drive range operation, main pressure isdirected td-the drive range passage-161 to feed the drive'rarige'circuit while main pressure remains available to the circuit previouslydescribed by supply of fluid by'the reverse-neutral-drive passage 162.Thus,

theverdrive unit lockout clutch 41 remains engaged while the drive rangecircuit is conditioned to effect transmission drive through the gearing.The drive range passage '161 directs main pressure to chambers 64 and 65to engage the forward drive clutch 58 with the outer chamber 64 beingfed through the flow restriction 163 to provide smooth shifting fromneutral to drive and also from park and reverse to drive. The driverange passage 161 also directs main pressure to the'governor valve 171to establish governor pressure in the governor passage 176. Thisgovernor pressure which increases with increasing vehicle speed isdirected to act the modulator passage l'7 8.is delivered by the detentcontrol valve 132 to the shift modulator I passage 230 which in turndirects this pressure to the 3-2 shift valve 311. The 3-2 shift valve 311 directs the modulator pressure to the shift modulator ll passage 280which in turn directs the fluid to the l-2 detent valve element 260 ofthe l-2 shift valve 258. The 1- 2 detent valve directs the fluid thusreceived; via passage 281 to chamber 282 where it acts rightward on the1 -2 regulator valve element 261againstthe, bias of spring 274. Theregulator valve element 261 movesrightward and admitspressurevia passage284 to the chamber 286 where the pressure therein which is thusregulated at a value less than and proportional to modulator pressure,acts to bias the l -2 shift valve element 259 towards its dovvnshiftposition. At some vehicle speed, the governorpres'sure bias willovercome the modulator pressure bias" to move the. l-2 shiftvalveelement- 259.- to its upshift position to deliver mainpressure fromthe drive range passage 161 to the2-3 drive passage266. Fluid is Idirected by the 2-3drive passage 266 through the flow on the l-2 shiftvalve 258, 2-3 shift valve 290, vacuum modulator valve 130 and overdrivegovernor pressure control valve 136. The governor pressure directed tothe modulator valve reduces modulator pressure with increases in vehiclespeed so that main pressure is regulated to vary with torque input tothe transmission for smooth shifts with sufficient capacity for bothheavy and light acceleration. Main pressure is also directed by thedrive range passage 161 to the 1-2 shift valve 258, the detent controlvalve 132, the 3-4 shift valve 324 and the 1-2 accumulator valve 460.The main pressure in-the drive range passage 161 is blocked at} the 1-2shift valve 258, the detent control valve 132 and the 3- 4 shift valve324 but at the l-2 accumulator valve 460 the bias provided by modulatorpressure acts tois conditioned in first-gear'and the vehicle may beaccelerated by advancing the engine throttle.

Drive Range-Secohd bear Drive a As the-vehicle is accelerated, governorpressure in chamber 2640f the l-2 shift valve 258 biases this valverestriction 454 to chamber 91 at a slow rate to engage the second gearbrake 96, the ball-valve 455 closing during flow in this direction. Thefluid passing through flow restriction 454 is also directed to chamber439 of the low and reverse brake servo 116 where it acts on the l-2accumulator piston 431 to stroke this piston upward against both thebias of spring 436 and the pressure bias provided by the l-2 accumulatorpressure present in chamber 441 as described previously, this 1- 2accumulator pressure which also may be described as trim pressure, beinga regulated pressure and increasing with increasing modulator pressureand thus torque demand. During such stroking of the l-2 accumulatorpiston 431, there is thus absorbed some of the fluid flow being used toapply the second gear brake 96 so that this brake-is applied at acontrolled rate dependent on the value of the l-2 accumulator pressure.This provides for smooth engagement of the second gear brake 96 with thebrake engagement occurring more rapidly at heavy torque demand than atlight torque-demand. In addition, the 2-3 drive passage 266isalsoconne'cted through the flow restriction 402 to chamber 384.0ftheoverrun brake servo 87 where such pressure acts to stroke the 2-3'accumulator piston 376 downward against the bias of spring 391. Thisstroking of the 2-3 accumulator piston 376 absorbs additional fluid fromthe overrun hand brake feed to further cushion engagement of the secondgear brake 96. At the overrun brake servo 87, the main pressure actingchamber 384 is not effective to stroke the overrun brake piston 374.since this pressure is balanced by the main pressurev present in thechamber 381 to permit the spring 388 to hold the piston 3'74 inits brakerelease position irrespective of the pressure present in chamber 384.

With both the'overdrive unit lockoutclutch 41 and forwarddrive clutch 58thus remaining engaged, and

the second-gear brake-96 now engaged, the transmission. is thusconditioned for second gear drive. At-the l- 2 shift valve 258 on theupshift to second gear, theshift modulator ll passage 2801s blocked andthe passage 281 downstream thereof is connected past land a of the a 1-2detent valve element 260 to;exhaus t. 272 so that only sp'ring'274 tendsto bias the l-2 shift valve to its downshift position. Thus a downshiftfrom second to first gear will occur at a vehicle speed lower than thatat Drive Range Third Gear Drive When operating in second gear drive, themodulator pressure in the shift modulator II passage 280 delivered tochamber 306 of the 2-3 shift valve 290 acts to bias this shift valve inits downshift position. With continuing vehicle acceleration and at somevehicle speed, governor pressure acting in chamber 295 on the 2-3 shiftvalve element 291 will bias this valve element against the modulatorbias to its upshift position to then admit main pressure from the 2-3drive passage 266 through flow restriction 298 to the direct driveclutch passage 296. Pressure in the direct drive clutch passage 296 isdirected to chamber 321 of the 3-2 shift valve 311 and depending uponthe value of modulator pressure in passage 230 acting on land b willposition the valve element 312 to connect the shift modulator I1 passage280 to the detent passage 204. With the detent control valve 132 in itsnon detent position, the detent passage 204 is connected to the low'drive range passage 166 which is exhausted at the manual valve 128 andthus the shift modulator II passage 280 is exhausted of modulatorpressure. Thus at light throttle, light torque demand operation theshift modulator ll passage 280 is exhausted. At heavy throttleconditions,

With the '3-4 shift valve 324 in its downshift position, modulatorpressure acts on land b of the 3-4 modulator valve element 327 toyieldingly hold the 3-4 shift valve 324 in its downshift position. Atsome vehicle speed, dependent upon modulator pressure and the bias ofspring 344, the 3-4 shift valve 324 will upshift to its overdriveposition. Due to the force of spring 344, governor pressure will notupshift the 3-4 shift valve 324 until a predetermined vehicle speed isreached.

Thus, at light throttle, minimum torque demand, a minimum vehicle speedis required for upshifting to overdrive even though overdrive may bedemanded by the 3-2 shift valve 311 may admit modulator pressure fromthe shift modulator I passage 230 to the shift modulator II passage 280,but in third gear drive, this modulator pressure is effective only uponsmall land 0 of the 2-3 modulator valve element 292 rather than thelarger land b to prevent undesirable hunting of the 2-3 shift valve.

The main pressure delivered to the direct drive clutch passage 296opensthe ball valve 407 so that fluid flows through flow restriction 408at a fast rate to chamber 75 of direct drive clutch 69 to commenceengagement of this clutch. Fluid is also delivered via flow restriction408 to chamber 386 of the overrun brake servo 87 where it, with theassistance of spring 391, strokes the 2-3 accumulator piston 376 upwardagainst the main pressure in chamber 384 and as a result provides forsmooth engagement of the direct driveclutch 69. With clutches 41, 58 andbrake 96 remaining engaged and now with the addedengagement of clutch69, the transmission is conditioned for direct drive.

Drive Range Overdrive or Fourth Gear Drive When operating in direct orthird gear drive, overdrive may be manually selected by the vehicleoperator, provided vehicle speed is above a predetermined minimum, byclosing switch 249. The valve element 246 then opens the exhaust port248 to drop'the pressure in chamber 242 of the overdrive governorpressure control valve 136 downstream of the flow restriction 244, thislatter flow restriction thus preventing loss of main pressure from themain passage 124. The main pressure in chamber 241 is theneffective tomove valve element 238 to the connect or governor pressure deliveryposition shown to admit governor pressure in governor passage 176 to the3-4 governor passage 254 and thus to chamber 338 of the 3-4 shift valve324.

the operator closing switch 249.

With the 3-4 shift valve 324 upshifted, modulator pressure is effectiveonly on the small land c of the 3-4- modulator valve element 327 toprevent hunting between overdrive and direct drive. The 3-4 shift valve324 then directs fluid from the drive range passage 161 through flow.restriction 330 to the overdrive brake passage 331 while connecting thelockout clutch passage 336 to exhaust port 340 through flow restriction339. The fluid in the overdrive brake passage 331 is directed to chamber53 to apply the overdrive brake 48 and is also admitted to chamber 359of the overdrive brake accumulator 135. The pressure thus. admitted tochamber 359 together with the bias'provided by spring 361 urges thepiston 354 upward against main pressure to discharge fluid in chamber358 intothe overdrive clutch passage 331. The stroking of piston 354 andthe flow restriction 339 at the 3-4 shift valve 324 cooperate to controlthe'rate of release. of .the lockout'clutch 41 and the rate ofapplication of the overdrive brake 48 to provide a smooth shifttransition. Upon completion of the establishment of overdrive, thepiston 354 acts as a valve to prevent main pressure in the main passage124 from reaching the lockout clutch passage 336. The main pressure isconstantly available from the main passage 124 through flow restriction369 to the overdrive brake accumulator and thus the valve action of thepiston 354 operates to prevent pressure loss while operating inoverdrive.

Drive Range Downshifting in overdrive, a normal closed or light throttledownshift, a heavy throttle downshift-and a detent or past full throttledownshift from overdrive to direct drive may occur. A light throttledownshift will occur at a substantially lower vehicle speed than thevehicle speed at which an upshift occurs since modulator pressure actsonsmall land 0 rather than the larger land b of the 3-4 modulator valveelement 327. Within a certain higher vehicle speed range, a heavythrottle forced downshift from overdrive to direct drive may occur dueto the efi'ect of modulator pressure on land 0 since the ,modulatorpressure is controlled by torque demand and vehicle speed. A detentdownshift may occurin a stillthan detent pressure and acts upon thesmaller land c of modulator valve element 327 to aid in biasing the 3-4;shift valve to its downshift'position. It will further be apparent thata downshift from overdrive to direct drive may be had at any time byopening switch 249 to exhaust governor pressure 4 shift valve 324.

Upon a downshift from overdrive to direct drive, the overdrive brakepassage 331 is exhausted through flow restriction .332 to the exhaustport 334 and the lockout clutch passage 336 is blocked from exhaust port340 by land to prevent exhaust of this passage by the 3.-.4 shift from'chamber'338 of the 3- i When operating in second gear drive, a lightthrottle valve 324. With exhaust of the overdrive brake passage 331, theoverdrive accumulator piston 354 is stroked by main pressure against thebias of spring 361 to force fluid in the accumulator chamber 359 throughflow restriction 332 to the exhaust port 334 of the 3-4 shift valve 324.Thus, the stroking of the piston 354 and the flow restriction332.cooperate to provide smooth engagement of the lockout clutch 41 andrelease of the overdrive brake 48 such that the downshift isaccomplished smoothly from overdrive to direct drive.

'With the transmission in third gear or direct drive, the 3-2 shiftvalve 311 normally connects the shift modulator Il passage 280 to thedetent passage 204 which is exhausted by the manual valve 128. Thus,normally no modulator pressure acts on the 2-3 shift valve 290 so that arelatively low speed is required for a downshift to second gear drive.Within a certain vehicle speed range, at heavy throttle operation,modulator pressure plus the bias of spring 319 exceed the main pressurebias provided by the pressure acting in chamber 321. to position thevalve element 312 to admit modulator pressure from shift modul ator Ipassage 230 to the shift modulator ll passage 280. At certain vehiclespeeds, the modulator thus provided to act on land 0 of the 2-3modulator valve element 292 will then position the 2-3 shift valve 290in its downshift position to connect the direct drive clutch passage 296to the reverse passage 168 which is then exhausted by the manual valve128. During the downshift from direct to the second gear drive, the ballvalve 407 closes flow restriction 408 so that the discharge of fluidfrom the clutch chamber 75 is through the flow restriction 409 at aslowrate. At the overrun brake servo 87. the accumulator piston 376 strokesagainst the spring 391 and cooperates with flow restriction 409 to delaythe. drop of pressure in chamber 75 so that the direct drive clutch 69is gradually released. This permits engage ment of the one-way brake 100without shock.

In a higher vehicle speed range, a detent of past full throttledownshift from third to-second gear drive may be had by closing switch225. The detent'control valve 132 is then forced to move to its detentposition to establish detent pressure in the detent passage 204 whereinthe modulator pressure in the shift modulator I passage 230 then becomesdetent pressure in shift modulator II passage 280 irrespective of theposition of the "3-2 shift" valve 311. This detent pressure acting uponlandc of the 2-3 modulator valve element 292 plus detent pressure fromthe detent passage 204 acting upon land b of this same valve elementwill position the 2-3 shift valve 290 in its downshift position athigher vehicle speeds than those required fora-heavy throttle forceddownshift below full engine throttle.

shift modulator II passage 280 is blocked by land a of the 1-2 detentvalve element 260 while the passage 281 is connected to the exhaust port272 and thus there is no modulator pressure effective on the valve fordownshift purposes. A past full throttle detent downshift may be had byclosing switch 225 whereupon detent control-valve 132 then deliversdetent pressure to the detentpassage 204 and thus to chamber 286' of the1-2 shift valve 258. This detent pressure in chamber 286.plus the biasof spring 274 moves the l -2 shift valve to its downshift position. Withthe l-2 shift valve in its downshift position, modulator pressure isthen admitted to act on the end of land b of theregulator valve element261 to maintain the. 1-2 shift. valve in its downshift position. Upon ashift from second to firstv gear drive, the 2-3 drive passage 266 isconnected to the exhaust port 267 by the 1-2 shift valve 258 and theball valve 455 opens flow restriction 456 to permit rapid exhaust fromchamber 91 to rapidly release the second gear brake 96. I 1

Intermediate Range I,

When the manual valve 128 is moved to the INT position to provide forintermediate range operation,

transmission operation is limited to providing first and second geardrive and also provides overrun braking in the second gear drive.

In intermediate range, the overdrive unit clutch 41- and the forwarddrive clutch 58 are applied in the same manner as described above indrive range first gear. Main pressure is now delivered by the manualvalve 128 to the intermediate range passage 164 which directs suchpressure to chamber 309 of the2-3 shift valve 290 where it acts on landb of the 2-3 shift valve element 291 to assistspring 300 in maintainingthe 2-3 shift valve in its downshift or second gear position. The

main pressure in intermediate range passage 164 is also delivered byball valve 209 to the main pressure regulathe overrun brake, the 2-3accumulator piston 376 will stroke against the spring 391 to cushion theapplication of the overrun brake band by. regulating the rate ofpressure rise in chamber 384 during the stroking of the piston 374. 1

1 In second gear in intermediate range operation, the main pressureacting on the 2-3 shift valve 290 prevents an upshift to third geardrive. Intermediate range operation is particularly useful forenginebraking purposes in descending long or steep grades, or inpreventing hunting between second and third gear drive when ascending agrade in a speed range wherein such hunting might otherwise occur.

Low Range Operation ment 461 and by ball valve 448 to chamber 438 of thelow and reverse brake servo 116.

In low range operation, main pressure is thus admitted by detent controlvalve 132 to the detent passage 204 and modulator pressure is regulatedat main pressure. Main pressure from the detent passage 204 istransmitted between lands a and b of the l-2 regulator valve element 261to chamber 286 to bias the 1-2 shift valve 258 to maintain the downshiftposition.

In addition, main pressure from the low range passage 1'66 acting onunbalanced land d of the l-2 shift valve element 259 acts to trim thedownshift forces on the l- 2 shift valve. Thus the transmission willremain in first gear until a much higher vehicle speed than that atwhich an upshift occurs when operating in drive range.

The main pressure delivered from the low range passage 166 to the 1-2accumulator valve 460 "acts upon the unbalanced area of land a to biasthe valve element 461 rightward so that main pressure is delivered tothe 1-2 accumulator passage 458 and thus to chamber 441 ofthe low andreverse brake servo 11 6.

In addition, main pressure is admitted by the ball valve 448 to thepassage 449 and thus to chamber 438 of the low and reverse brake servo116. Thus, in applying the brake band 115 the piston 426 moves againstthe bias provided by main pressure in the accumulator chamber- 441 andthe force of both of the springs 429 and 436 as it strokes toward itsband apply position. This provides a smooth brake band engagement toestablish the low drive.

- some vehicle speed higher than that at which a first to second gearshift occurs when operating in. intermediate or drive range, the l-2shift valve 258 upshifts to its second gear position. At the 2-3 shiftvalve 290, main pressure from the intermediate range passage 164 acts inchamber 309 on land b of the 2-3 shift valve element 291 to keep it inthe downshift position. In low range second gear drive, the clutches 41and 58 and the overrun brake 86 are engaged and the brake band 115 isreleased, brake 115 being released by main pressure being admitted tothe low and reverse brake servo chamber 439 and the main pressure inaccumulator chamber 441. The overrun brake 86 is applied by mainpressure admitted to chamber 384 of the overrun brake servo 87 by the2-3 drive passage 266'. The lockout clutch 41 and the forward driveclutch 58 are applied in the same manner as in drive range second gearoperation. In low range operation, the main pressure is boosted abovenormal main pressure as in intermediate range operation.

Reverse When the manual 'valve 128 is moved to its reverse position toprovide reverse transmission operation, theclutches 41, 69 and brakeband 115 are engaged. Clutch 41 is engaged in the same manner as inneutral and all of the previously described drives. The drive suresupply and the 2-3 shift valve thus delivers main I pressure from thereverse passage 168 to chamber so that main pressure in both chambers 75and 76 acts to engage the direct drive clutch 69. Main pressure isdelivered from the reverse drive passage 168 by the ball valve 448 tochamber 438 of the low and reverse brake servo 116 to thus effectengagement of the brake band 1 15. In reverse operation, modulatorpressure from the passage 178 acts on boost member 142 of the mainpressure regulator valve 126 and main pressure from the reverse passage168 also acts on this boost member to boost main pressure. In reverse,the main pressure is thus regulated at a higher range of pressure thanthat in drive range operation. This pressure boost in reverse assuresthat the clutches 41, 69 and hand brake will not slip.

The above described embodiment is illustrative of the invention whichmay be modified within the scope of the appended claims.

I claim:

1. In a control system for an automatic transmission the combination oftransmission means including multiratio gearing and a plurality of fluidpressure operated drive establishing means for providing a plurality ofdifferent transmission drives to drive a load on selective delivery offluid pressure to said fluid pressure operated drive establishing means,a source of fluid pressure, governor valve means operatively connectedto said fluid pressure source for providing a governor pressure thatchanges with load speed, modulator valve means operatively connected tosaid fluid pressure source for providing a modulator pressure thatchanges with load torque demand, a plurality of shift valve meansresponsive to both said governor pressure and said modulator pressurefor selectively delivering fluid from said source to said fluid pressureoperated drive establishing means to effect establishment of saidtransmission drives and also automatic shifting between saidtransmission drives in response to changes in load speed and load torquedemand, overdrive governor pressure control valve means operable in anoverdrive sh'ift permit position to deliver governor pressure to act onsaid shift valve means that effects establishment of overdrive toprovide for shifting to said overdrive and operable in an overdrivesolenoid valve means for conditioning said overdrive governor pressurecontrol valve means in said overdrive shift permit position.

2. in a control system for an automatic transmission the combination oftransmission means including multiratio gearing and a plurality of fluidpressure operated drive establishing means for providing a plurality ofdifferent transmission drives including an overdrive anda plurality oflower speed drives to drive a load with said lower speed drives beingestablished by delivery of fluid pressure to one of said fluid pressureoperated'drive establishing means, exhaust of another of said fluidpressure operated drive establishing means and sel'ec tive fluidpressure delivery to the remaining fluid pressure operated driveestablishing means and with said overdrive being established on exhaustof said one fluid pressure operated drive establishing means anddelivery of fluid pressure to said another fluid pressure operated driveestablishing means while fluid pressure delivery is maintained to one ofsaid remaining fluid pressure operated drive establishing means, asource of fluid pressure, governor valvemeans operatively connected tosaid fluid pressure source for providing a governor pressure thatchanges with load speed, modulator valve means operatively connected tosaid fluid pressure source for providing a modulator pressure thatchanges with load torque demand, overdrive accumulator means fornormally delivering fluid pressure from said source to said one fluidpressure operated drive establishing means, a plurality of shift valvemeans in-' cluding overdrive shift valve means responsive to both saidgovernor pressure and said modulator pressure for selectively deliveringfluid from said source to the remaining fluid pressure operated driveestablishing means to effect establishment of said transmission drivesand automatic shifting between said transmission drives in response tochanges in load speed and load torque demand, said overdrive accumulatormeans being responsive to the pressure supplied by.the said shift valvemeans that establishes said overdrive to prevent delivery of fluidpressure from said source to said one fluid pressure operated driveestablishing means and also to determine the rate of pressure buildup inthesaid another fluid pressure operated drive establishing meansengaging said overdrive, overdrive governor pressure control valve meansoperable in an overdrive shift permit position to deliver governorpressure to act on said overdrive shift valve means that effectsestablishment of said overdrive to permit shifting to said overdrive andin an overdrive shift prevent position to prevent delivery of saidgovernor pressure to 28 tiratio gearing and a plurality of fluidpressure operated drive establishing means for providing a plurality ofdifferent transmission drives including an overdrive on selectivedelivery of fluid pressure to said fluid pressure operated driveestablishing means, said gearing including an overdrive unit and saidfluid pressure operated drive establishin means including a lockup servowhich when supp red with fluid pressure locks up said overdrive gearingfor the establishment of all transmission drives in speed ranges lowerthan overdrive and further including an overdrive servo that operates ondelivery of fluid pressure thereto to condition said overdrive unit toestablish said overdrive, a, source of fluid pressure, governor valvemeans operatively connected to said vfluid pressure source forprovidinga governor pressure that changes with load speed, modulato't valve meansoperatively connected to said fluid pressure source for providing amodulator pressure that changes with load torque demand, a plurality ofshift valve means responsive to both said governor pressure and saidmodulator pressure for selectively delivering fluid from said source tosaid fluid pressure operated drive establishing means to effectestablishment of said transmission drives and automatic shifting betweensaid transmission drives in response to changes in load speed and loadtorque demand, said shift valve means including overdrive shift valvemeans operable in a downshift position to exhaust said overdrive servoof pressure and in an upshift position to deliver pressure from saidsource to said overdrive servo while exhausting said lockup servo,spring means normally biasing said overdrive shift valve means to saiddownshift position, overdrive governor pressure control valve meansoperable in an overdrive shift prevent position to prevent governorpressure from acting on said overdrive shift valve means and in anoverdrive shift permit position permitting governor pressure to act onsaid overdrive shift valve means, spring means normally biasing saidoverdrive governor pressure control valve means to said shift preventposition, first pressure bias means supplied with fluid pressure fromsaid source during engagement of all said transmission drives to biassaid overdrive governor pressure control valve means against said springbias to said shift permit position, second pressure bias means suppliedwith fluid pressure from said source for assisting said spring means tobias said overdrive governor pressure control valve means to said shiftprevent position to overcome the oppositely acting pressure biasprovided by said first pressure bias means, overdrive solenoid valvemeans operable to normally permit said second pressure bias means tobias said overdrive governor pressure control valve means to said shiftprevent position and being manually operable to relieve said secondpressure bias means to effect movementof said overdrive governorpressure control valve means to said shiftpermit position to permitshifting to said overdrive.

set er:

1. In a control system for an automatic transmission the combination oftransmission means including multiratio gearing and a plurality of fluidpressure operated drive establishing means for providing a plurality ofdifferent transmission drives to drive a load on selective delivery offluid pressure to said fluid pressure operated drive establishing means,a source of fluid pressure, governor valve means operatively connectedto said fluid pressure source for providing a governor pressure thatchanges with load speed, modulator valve means operatively connected tosaid fluid pressure source for providing a modulator pressure thatchanges with load torque demand, a plurality of shift valve meansresponsive to both said governor pressure and said modulator pressurefor selectively delivering fluid from said source to said fluid pressureoperated drive establishing means to effect establishment of saidtransmission drives and also automatic shifting between saidtransmission drives in response to changes in load speed and load torquedemand, overdrive governor pressure control valve means operable in anoverdrive shift permit position to deliver governor pressure to act onsaid shift valve means that effects establishment of overdrive toprovide for shifting to said overdrive and operable in an overdriveshift prevent position to prevent delivery of said governor pressure tosaid shift valve means that establishes said overdrive to preventshifting to said overdrive, means for normally biasing said overdrivegovernor pressure control valve means to said overdrive shift preventposition, and manually controlled overdrive solenoid valve means forconditioning said overdrive governor pressure control valve means insaid overdrive shift permit position.
 2. In a control system for anautomatic transmission the combination of transmission means includingmultiratio gearing and a plurality of fluid pressure operated driveestablishing means for providing a plurality of different transmissiondrives including an overdrive and a plurality of lower speed drives todrive a load with said lower speed drives being established by deliveryof fluid pressure to one of said fluid pressure operated driveestablishing means, exhaust of another of said fluid pressure operateddrive establishing means and selective fluid pressure delivery to theremaining fluid pressure operated drive establishing means and with saidoverdrive being established on exhaust of said one fluid pressureoperated drive establishing means and delivery of fluid pressure to saidanother fluid pressure operated drive establishing means while fluidpressure delivery is maintained to one of said remaining fluid pressureoperated drive establishing means, a source of fluid pressure, governorvalve means operatively connected to said fluid pressure source forproviding a governor pressure that changes with load speed, modulatorvalve means operatively connected to said fluid pressure source forproviding a modulator pressure that changes with load torque demand,overdrive accumulator means for normally delivering fluid pressure fromsaid source to said one fluid pressure operated drive establishingmeans, a plurality of shift valve means including overdrive shift valvemeans responsive to both said governor pressure and said modulatorpressure for selectively delivering fluid from said source to theremaining fluid pressure operated drive establishing means to effectestablishment of said transmission drives and automatic shifting betweensaid transmission drives in response to changes in load speed and loadtorque demand, said overdrive accumulator means being responsive to thepressure supplied by the said shift valve means that establishes saidoverdrive to prevent delivery of fluid pressure from said source to saidone fluid pressure operated drive establishing means and also todetermine the rate of pressure buildup in the said another fluidpressure operated drive establishing means engaging said overdrive,overdrive governor pressure control valve means operable in an overdriveshift permit position to deliver governor pressure to act on saidoverdrive shift valve means that effects establishment of said overdriveto permit shifting to said overdrive and in an overdrive shift preventposition to prevent delivery of said governor pressure to said overdriveshift valve means to prevent shifting to said overdrive and manuallycontrolled overdrive solenoid valve means for selectively conditioningsaid overdrive governor pressure control valve means in said overdriveshift permit and shift prevent positions.
 3. In a control system for anautomatic transmission the combination of transmission means includingmultiratio gearing and a plurality of fluid pressure operated driveestablishing means for providing a plurality of different transmissiondrives including an overdrive on selective delivery of fluid pressure tosaid fluid pressure operated drive establishing means, said gearingincluding an overdrive unit and said fluid pressure operated driveestablishing means including a lockup servo which when supplied withfluid pressure locks up said overdrive gearing for the establishment ofall transmission drives in speed ranges lower than overdrive and furtherincluding an overdrive servo that operates on delivery of fluid pressurethereto to condition said overdrive unit to establish said overdrive, asource of fluid pressure, governor valve means operatively connected tosaid fluid pressure source for providing a governor pressure thatchanges with load speed, modulator valve means operatively connected tosaid fluid pressure source for providing a modulator pressure thatchanges with load torque demand, a plurality of shift valve meansresponsive to both said governor pressure and said modulator pressurefor selectively delivering fluid from said source to said fluid pressureoperated drive establishing means to effect establishment of saidtransmission drives and automatic shifting between said transmissiondrives in response to changes in load speed and load torque demand, saidshift valve means including overdrive shift valve means operable in adownshift position to exhaust said overdrive servo of pressure and in anupshift position to deliver pressure from said source to said overdriveservo while exhausting said lockup servo, spring means normally biasingsaid overdrive shift valve means to said downshift position, overdrivegovernor pressure control valve means operable in an overdrive shiftprevent position to prevent governor pressure from acting on saidoverdrive shift valve means and in an overdrive shift permit positionpermitting governor pressure to act on said overdrive shift valve means,spring means normally biasing said overdrive governor pressure controlvalve means to said shift prevent position, first pressure bias meanssupplied with fluid pressure from said source during engagement of allsaid transmission drives to bias said overdrive governor pressurecontrol valve means against said spring bias to said shift permitposition, second pressure bias means supplied with fluid pressure fromsaid source for assisting said spring means to bias said overdrivegovernor pressure control valve means to said shift prevent position toovercome the oppositely acting pressure bias provided by said firsTpressure bias means, overdrive solenoid valve means operable to normallypermit said second pressure bias means to bias said overdrive governorpressure control valve means to said shift prevent position and beingmanually operable to relieve said second pressure bias means to effectmovement of said overdrive governor pressure control valve means to saidshift permit position to permit shifting to said overdrive.